Photo

NOAO says the Bubble Nebula (NGC7635) "is one of three shells of gas surrounding the massive star BD+602522, the bright star near the center of the bubble. Energetic radiation from the star ionizes the shell, causing it to glow. About six light-years in diameter, the Bubble Nebula is located in the direction of the constellation Cassiopeia."
— T.A. Rector/University of Alaska Anchorage, H. Schweiker/WIYN and NOAO/AURA/NSF